At least 15 people were shot, including two who were critically injured, when a gunman opened fire during a Halloween celebration in Chicago early Sunday morning.

The gunman fired shots into the gathering just after 1 a.m. in the Lawndale neighborhood on the city’s West Side, police said.

Police who responded to the shooting saw a male suspect firing rounds into the crowd before fleeing on foot.

The suspect, who has not been identified, was later arrested, and a firearm was recovered by officers, ABC 7 reported.

Partygoers told the outlet that a fight broke out in the backyard and one of the individuals involved was asked to leave.

After refusing to leave, the man allegedly began shooting.

One witness, Andre Williams, said he knew at least three people who had gotten shot during the event.

“They told him he couldn’t come in, and he must have gone to his car and come back and started shooting,” Williams said. “A couple people got hit. Three people that I know got hit.”

Six women and nine men were shot during the Halloween party, police and witnesses reportedly said.

The victims’ ages ranged from 26 to 53 years old, according to the outlet.

Two of the victims, a 26-year-old woman and a 48-year-old man were taken to the hospital in critical condition.

The other victims were listed as being in good condition at various hospitals.

Police are investigating what led to the shooting.

It came after Halloween celebrations in Tampa and Indianapolis were also marred by mass shootings overnight.